If the erosion of individual privacy began long before 2001, it has accelerated enormously since. And by no means always to bad effect: suicide-bombers, by their very nature, may not be deterred by a CCTV camera (even a talking one), but security wonks say many terrorist plots have been foiled, and lives saved, through increased eavesdropping, computer profiling and “sneak and peek” searches. But at what cost to civil liberties?

Privacy is a modern “right”. It is not even mentioned in the 18th-century revolutionaries’ list of demands. Indeed, it was not explicitly enshrined in international human-rights laws and treaties until after the second world war. Few people outside the civil-liberties community seem to be really worried about its loss now.

That may be because electronic surveillance has not yet had a big impact on most people’s lives, other than (usually) making it easier to deal with officialdom. But with the collection and centralisation of such vast amounts of data, the potential for abuse is huge and the safeguards paltry.

Ross Anderson, a professor at Cambridge University in Britain, has compared the present situation to a “boiled frog”—which fails to jump out of the saucepan as the water gradually heats. If liberty is eroded slowly, people will get used to it. He added a caveat: it was possible the invasion of privacy would reach a critical mass and prompt a revolt.